Hydrodynamic compliant thrust bearing

ABSTRACT

A resilient compliant hydrodynamic fluid film thrust bearing includes a top bearing sheet of thin metalic foil material, and a lower supporting sheet of the same or slightly heavier gauge material. The top bearing sheet is stamped to produce an annular array of truncated sector-shaped flaps attached to the array along one radially extending edge. The second section is stamped to produce an annular pattern of raised projections formed by bending the material along slits to form radially extending bumps which resiliently support the first section. The two sheets are superimposed and aligned, and are welded together along the edge by which the sector-shaped flaps are attached to the first section. The welded assemblies are then sheared from the superimposed foils and deburred.

BACKGROUND OF THE INVENTION

Compliant hydrodynamic fluid film bearings have been proven in use toprovide extremely low friction durable, reliable support for ultra-highspeed rotors in the most hostile environments, such as very low or veryhigh temperatures, in which conventional lubrication fails. Theseapplications are generally custom designed for small volume uses andthey have usually been correspondingly expensive. For this reason,bearings of this class have acquired a reputation in the art asultra-sophisticated, high technology products which are not suitable forordinary consumer products wherein cost is a major consideration.

Although the ultra-high speed and hostile environment capabilities ofthe hydrodynamic fluid bearings have made the sophisticated applicationsan important field of use, I believe that the true potential forbearings of this nature will ultimately be in ordinary industrial,automotive and consumer products. I have designed processes forproduction of compliant hydrodynamic fluid film bearings to make highvolume production of these bearings extremely economical, even more sothan conventional bearings.

SUMMARY OF THE INVENTION

A compliant hydrodynamic thrust bearing includes a thin, flexiblebearing sheet supported on a compliant support element that deflects andpermits the bearing sheet to deflect and conform to the bearing surfaceof the thrust runner where it deviates during operation from trueparallelism with the thrust plate, under the influence of thermaldistortion or runout caused by externally applied loads or rotorimbalance.

The operation of a compliant hydrodynamic fluid film thrust bearing isbased on the generation of a supporting fluid film in the gap betweenthe thrust runner and the bearing sheet. This occurs because theboundary layer of fluid adjacent to the rotating thrust runner is drawninto the gap, which is slightly wedge-shaped, tapering in the directionof thrust runner rotation. The fluid film in the wedge-shaped gap buildsin pressure toward the trailing edge of the gap, thereby providing athin pressurized supporting cushion of fluid between the bearing sheetand the thrust runner.

The support member is made more compliant than the fluid film so thatthe support member will deflect under transient excursions of the thrustrunner before the fluid film is breached. The support member should beable to deflect locally without causing changes in the elevation of itsother portions, which could raise the bearing sheet in those otherportions and create "hot spots" or local areas on the bearing sheet whenthe pressure exceeds the load carrying capacity of the fluid film andthe bearing sheet contacts the thrust runner. This can result in a holeburned instantaneously through the bearing sheet, with detrimentalconsequences to the load carrying capacity of the bearing.

Accordingly, it is an object of this invention to provide a complianthydrodynamic fluid film thrust bearing which permits the bearing sheetto deflect locally without affecting its elevation elsewhere. Thisbearing is also extremely economical to produce in great numbers andprovides the advantages of hydrodynamic fluid film thrust bearings, viz.low friction, durability, ultra-high speed, and reliable operation. Thetooling for manufacturing the bearing according to this invention is notof such high cost that it constitutes a significant capital investment,so a reasonable investment can produce tooling for an entire line ofbearings from very small to very large. Another object of this inventionis to provide a method of economically manufacturing a complianthydrodynamic fluid film thrust bearing in great quantities. This methodenables the same tooling to be used for manufacturing an entire familyof bearings having different characteristics, and assures the exactalignment and circularity of the bearing sections.

The invention contemplates a method for producing a bearing assembly,and the bearing assembly itself, fabricated from two strips of metal.Using punch and die techniques in a standard automatic press, a circularpattern of truncated sector-shaped flaps or pads is stamped into thefirst strip leaving a vane along one radial edge of the flap by which itremains attached to (i.e. unsevered from), the strip. The second striphas an annular formation of radial slits stamped therein, and thematerial on the edges of the slits is bent away from the plane of thestrip to form radially extending resilient bump projections. The slitsare arranged in a plurality of clusters separated by solid zones. Thetwo strips are then superimposed with the circular patterns, the pads,and the vanes in the first strip aligned with the circular patterns, theclusters of slits, and the solid zones, respectively, in the secondstrip. The vane and the solid zone are then spot or seam welded and thewelded assembly is sheared from the superimposed strips.

DESCRIPTION OF THE DRAWINGS

These and other objects of the invention and the invention itself willbe more clearly understood upon reading the attached description of thepreferred embodiment in conjunction with an examination of the appendeddrawings, wherein

FIG. 1 is a plan view of a bearing surface strip made according to thisinvention;

FIG. 2 is a plan view of a resilient support strip made according tothis invention;

FIG. 3 is a perspective exploded view showing the two strips of FIGS. 1and 2 aligned and ready to be superimposed;

FIG. 4 is a plan view of the superimposed and welded strips shown inFIGS. 1 and 2 prior to shearing from the strip;

FIG. 5 is an elevation taken along lines V--V in FIG. 4.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring now to the drawings wherein like reference charactersdesignate identical or corresponding parts, and particularly to FIG. 1thereof, a metal strip 10 is shown having a plurality of circularsections 12 stamped therein. A second metal strip 14, shown in FIG. 2has a plurality of sections 16 stamped therein corresponding indimension to the sections 12 in strip 10. After the sections 12 and 16are stamped in the strips 10 and 14, the strips are superimposed andaligned as shown in FIG. 3 and are spot or seam welded together in themanner shown in FIG. 4 to produce a series of bearing assemblies 18which are then sheared from the superimposed sheets 12 and 14 asfinished thrust bearing assemblies.

Referring again to FIG. 1, the strip 10, which may be of materials suchas stainless steel or Inconel, is passed through a metal punch press(not shown) which includes correspondingly shaped punch and die membersto shear the outline of a plurality of truncated sector-shaped flaps orpads 20 (six being shown) in the metal strip 10. This operation producessix truncated sector-shaped pads, each having an upwardly facing bearingsurface 21. The pads are sheared on three sides and attached to thesheet by small retention tabs 24 at the inner and outer circumferentialedges of the pads 20.

In the same operation in which the section 12 is stamped in the sheet10, the pads 20 are slightly bent at a predetermined radial bend 26 sothat the flaps protrude or extend from the sheet 10 in the manner shownin FIGS. 3 and 5. The radial vane 28 between the bend line 26 and theadjacent radial edge of the pad 20 remains in the plane of the sheet 10and constitutes a weld strip along which the section 12 is welded to thesection 16, as shown in FIGS. 4 and 5. The bend line 26 is the leadingedge of a ramp 29 for the pad 20 which is productive of the hydrodynamicsupporting fluid wedge which is generated over each pad 20 by therelative movement of a thrust runner 30 moving clockwise as shown by thearrow 31 in FIG. 5 over the bearing assembly 18, as discussed below.

Referring now to FIG. 2 the strip 14 which may be of the same materialas the strip 10, or of slightly thicker gauge, is passed through aseparate metal punch press. In this operation the outline of theresilient support sections 16 are sheared, and the slits 36 are sheared,although the slits may be sheared in a separate operation. This producesa series of areas 32 separated by retention tabs 34 which retain thestamped section 16 in the strip 14 until it is to be removed. Each tab34 coincides with the outer end of a radial vane 35 which separates theareas 32 and constitutes a weld strip to which a respective vane 28 onstrip 10 is later welded. The support areas 32 each include a cluster ofslits 36 which extend radially in the annular section 16. When the slitsare formed, the material adjacent slit 36 is deformed away from theplane of the strip 14 in the form of a raised projection or split bump38 shown in FIGS. 3 and 5. The two longitudinal portions on each side ofthe slit 36 can deflect independently of each other and the rest of thesection 16 so that, in operation, deflection of the bump or bumps in onearea of the section 16 will not cause elevations or other changes in anyother part of the section 16. The height of the bumps 38 can begraduated from low height adjacent the leading edge 26 of the pad, andgradually increasing in height toward the last bump in area 32. Thisarrangement facilitates the inclined orientation of the pads 20 whenthey are welded to the weld vane 35 between the areas 32 to facilitatethe generation of load-supporting hydrodynamic fluid wedges. The centerplug can be punched out of the section 16 during the initial shearingoperation, leaving a circular hole 40.

After the two strips have been sheared in the manner indicated above,while the sections 12 and 16 are still in the strips 10 and 14 andbefore welding, they may be heat treated in a furnace, in a knownmanner, for hardening and resilience, and coated with anti-frictioncoating such as molybdenum disulfide, Teflon or "HL-800" a proprietaryanti-friction coating of Mechanical Technology Incorporated of Latham,N.Y. HL-800 is a hard thin coating of a graphite and cadmium oxidemixture in a ceramic matrix that provides good anti-frictioncharacteristics at high temperature. Its functions and method ofapplication are disclosed in the co-pending application Ser. No. 974,264entitled "High Temperature Low Friction Surface Coating" of BharatBhushan, filed concurrently herewith the disclosure of which is herebyincorporated by reference. The coating of anti-friction material on thebearing surfaces 21 of the first strip 10 is best accomplished bysuperimposing a mask on the zone 12 which covers everything but thetruncated sector-shaped pads 20. The radial vane 28 is also covered tofacilitate welding in the next step.

The strip 10 and the strip 14, after shearing, heat treating, andcoating with anti-friction material, are superimposed and aligned withthe use of alignment apertures 44. These apertures may also be used toinsure that the patterns 12 and 16 are accurately stamped on the strips10 and 14. The alignment automatically positions the pads 20 over theirrespective clusters of bumps 38 and aligns the weld vanes 24 of sections12 over the weld vanes 35 on sections 16. The welding is accomplished bya welding jig which produces a series of spot welds in radial patternsalong the weld vanes 24 and 35 as shown in FIG. 5, or seam welds acontinuous weld line along these vanes. The welding operation can befollowed immediately by, or by simultaneous with, the next operationwhich is to shear the welded assembly of sections 12 and 16 from thestrips 10 and 14.

The welded assembly, shown in FIGS. 4 and 5, may have shear burrs on theedges of the pad 20 and on the circumferential edges of the section 16.The burrs on the pad 20 face downwardly and lie radially and angularlybeyond the supporting bumps 38, so that these burrs do not interferewith the operation of the thrust bearing. The burrs on the slits 36 canbe made to be on the underside of the bumps, and therefore not interferewith the interaction between the pads 20 and the bumps 38. The burrs onthe outer and inner circumferential edges of the section 16 would alsoface downwardly and might interfere with the seating of the bearingassembly on the thrust plate 42. Therefore it might be desirable toprocess the bearing assembly 18 through a polishing machine to removethe burrs on the lower face of the assembly.

An automated continuous operation to manufacture the bearing disclosedherein can be accomplished with three punch presses, an automaticwelding machine and a heat treatment furnace. The strips 10 and 14 canbe processed simultaneously in two parallel lines by two punch pressesand the strips, still in the form of strips, can be passed into thewelding machine where they are aligned and welded along the vanes 28 and35. The superimposed and welded strips 10 and 14 are then passed to thethird press which, also utilizing the aligning apertures 44, shears thebearing assemblies from the sheets 10 and 14. The bearing assemblies canthen be heat treated and coated, as described previously.

Since very little material is sheared in the final step, namely, theretention tabs 24 and 34, the bearing assembly 18 is subjected to verylittle force and therefore is not subjected to damage by the finalshearing step. Moreover, the final shearing step need include onlyshearing points at the six angular locations around the bearing assembly18, and these locations are at the weld ribs 28 and 35, which arebetween the aligned pads 20 and supporting bump clusters 32. Thereforethe areas of the bearing assembly 18 which could otherwise be damaged bya shearing step after the sections 12 and 16 are welded together are notdamaged because these delicate areas are not subject to shear forces.

A typical bearing to be manufactured by the disclosed process employsInconel X-750 sheet metal, typically 0.003-0.004 inches thick and, afterheat treating, having a hardness of approximately 50 Rockwell C. Theoutside diameter of the bearing is approximately 1.5 inches and sixbearing pads are provided in this example.

The disclosed method reliably and consistently produces bearings whichare perfectly circular and whose pads 20 and support zones 32 areprecisely aligned angularly and radially, and does so with significantproduction economics. The tooling which is used to fabricate thedisclosed bearing can be used on materials other than the materialsdisclosed. For example, in an application in which the thrust loads willbe greater than those intended to be borne by the disclosed embodiment,material of greater thickness and strength can be employed to providestiffer support zones 32 and stiffer pads 20. In addition, the pressesand welding machine setup can be employed with different size punches toenable the production process to run continuously. That is, after abearing of particular size and stiffness is produced in sufficientquantity to satisfy the demand for a period of time, the presses may beprovided with punches and dies of a different size and spacing, and thewelding machine electrodes may be repositioned, so that thrust bearingsof a different dimension may be fabricated using the same presses andwelding machine. The capital investment for the presses and weldingmachine is not high considering that a complete line of bearings of thisdesign of different diameters and stiffnesses can be produced from thistooling. In addition, the same presses could be utilized to fabricate,from the same metal strips, bearings of the design disclosed in myco-pending application Ser. No. 974,254 entitled "Modular CompliantHydrodynamic Bearing with Overlapping Bearing Sheet" filed concurrentlyherewith.

The method disclosed herein is so uncomplicated and is so conducive toprecision operation that the bearing assemblies produced can be heldwithin very narrow tolerance limits. It is thus possible to produce ahigh precision bearing in a fully automated process productive of veryfew, if any, defective bearings, and using a production line requiringrelatively small capital investment. It produces a convenient,inexpensive welded assembly which is easily handled and inspected andwhich can be easily mounted onto a product by clamping, welding, cement,and/or automatic assembly technique.

Obviously, numerous modifications and variations of the disclosedembodiment of the invention are possible in light of this disclosure.For example, the radial slits 36 could be separated by other radialslits which extend only across the order halt of the radius of thesection 16 to help equalize the stiffness of the support zones 32 in theradial direction. It is to be expressly understood, therefore, thatthese and other modifications are to be considered as part of myinvention which is defined by the spirit and scope of the appendedclaims, wherein

I claim:
 1. A compliant hydrodynamic fluid film thrust bearing forpositioning within a gap defined between the opposed surfaces of athrust plate and a relatively rotating thrust runner, and fastening tosaid thrust plate, comprising:(a) a first annular section having aplurality of angularly adjacent, truncated, sector-shaped pads of thin,flexible sheet metal, each attached to the bearing along one radial edgeportion, said radial edge portion being the leading edge with respect tothe direction of rotation of the thrust runner, and (b) a second annularsection underlying and supporting said first annular section, and havinga plurality of slits, each slit forming at least one edge of a resilientprojection elevated above the plane of said second annular section, saidslits being distributed around said second section in a plurality ofangularly spaced clusters which are angularly aligned with saidsector-shaped pads to provide resilient support for said pads.
 2. Thebearing defined in claim 1, wherein said projections are radiallyelongated and said angular spacing of said clusters provides radialvanes therebetween, along which vanes said radial edge portions of saidpads are attached.
 3. The bearing defined in claim 2, wherein said slitsrun longitudinally along the crest of said projections.
 4. The bearingdefined in claim 1, where said projections in each of said clustersincrease in height from the projection nearest said radial edge portionof the respective pad over said cluster toward the projection nearestthe angularly remote edge of said pad.
 5. The bearing defined in claim1, wherein each of said projections is compliant independently of theother projections and the other portions of said second section.
 6. Thebearing defined in claim 5, wherein said projections are more compliantthan the fluid film generated over said bearing by rotation of saidthrust runner.
 7. The bearing defined in claim 6, wherein saidprojections each extend radially along said second section, said padsbeing supported for substantially their entire radial extent by saidprojections.
 8. The bearing defined in claim 7, wherein said projectionsin each of said clusters increase in height from the projection nearestsaid radial edge portion of the respective pad over said cluster towardthe projection nearest the angularly remote edge of said pad.